A massive chunk of Antarctica’s fastest-moving ice stream, the Pine Island Glacier, dropped into the Amundsen Sea this week, nearly two years after scientists first observed a crack in the glacier tongue.

German scientists, who have been tracking the progress of the ice mass since NASA satellites first observed the crack in October, 2011, say the calved iceberg measured 720 square kilometers (278 square miles), or about the size of the city of Hamburg. There is no conclusive proof that climate change triggered the ice break, said Angelika Humbert, an ice researcher at the Alfred Wegener Institute. But shifting wind patterns around Antarctica are bringing warmer waters to the surface of the Southern Ocean in West Antarctica, which is hastening the thinning of some glaciers. Humbert said those warmer waters are causing the Pine Island Glacier to flow more rapidly into the Amundsen Sea — about 4 kilometers per year. The Pine Island Glacier is moving faster and discharging more ice into the sea than any other glacier on the continent, in part because of rising global temperatures, according to other scientists. If the entire West Antarctic ice sheet flowed into the ocean, it could cause sea levels to rise by about 3.3 meters globally, scientists say.